Please
note, if any member wishes to add an item to the next agenda,
or has a news item that they think will be of interest to club members,
or wishes to dispose of any item of equipment, please email to that
effect on the Club Members Reflector.

Steve
Wyatt M0OXR, is an active member of the club and offers below some information
and advice on an item of equipment well known to many older members but now
may be available at cheap second hand prices
BIRDs
of a feather….
This
short article is designed to familiarise the reader with some of the products
made by the Bird Electronic Company of
The
main task for most of their products is RF power measurement. The meters
usually encountered at rallies consist of a line section, moving coil meter,
range element, and for some models, a means of indicating peak levels with
additional circuitry. Common to all these is an aluminium die-cast case.
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In Photo 1, you can see the heart of the Rf meter, the line section.
This is made of a cast brass body, which is silver plated. On top
is the connector to the moving coil meter (via a screened cable), and in
front, the entry port of the range element, more of which later.
At each end is the Rf connector to which your co-axial cable
transmission line is attached. At
first glance, it appears to be a standard N-type. But looking closer
shows it to have a larger than normal flange. This means that you will
have to buy their connectors if you want to change to an alternative
type (there are 26 different flange-mounted sockets and plugs
available).Of course, it is possible to use commonly available adaptors,
but this can lead to impedance matching problems. To change the flange
connector, four screws need to be removed, and it’s then pulled out.
The Bird ones cost about 8 times that of standard flange types. Being an
in-line device, the meter can read forward and reflected power, by
reversal of the element. Although not directly calibrated in VSWR, a
graph is supplied with the meter where it can be read off, after both
forward and reverse readings are taken. |
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As well as antennas, dummy loads can be attached directly to the
output side. Photo
3 shows a few examples of Bird loads. Two types are shown: the black
ones are dry loads, meaning they convect the
heat away by ‘heat sink ’technique. The connectors are fixed N-type
on the smaller models, but may be changed on the larger ones. Care
should be taken if dismantling, as some contain a resistor made of
beryllium oxide, a toxic substance.
The larger grey-paint finish unit uses mineral oil
(oil-dielectric) to dissipate the heat along with traditional fins. For
a given physical size the oil-filled type has a
greater power dissipation. The connector is interchangeable. |
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The remaining photos show
examples of some Bird Rf power meters. Photo
5 is of the most well-known model, the 43.Composed of line section,
meter, element and case, the accuracy is quoted as +- 5% of full scale
deflection (fsd). This
is the most commonly seen model, and has become an industry standard,
being introduced in 1952. Photo
7 is a more sophisticated version, model 4314B.This can read both
average carrier wave and peak power levels. It uses the same elements as
the 43 (fortunately!). It
does, however, require battery power to work. Accuracy is +-8% peak
+-5% CW. Photo
8 is a multi-power range model, 4410A.This
uses a different range of elements, but has a switched scale to allow
many power levels to be measured on any one element.
Accuracy is +-5%(CW only). Photo
4 shows the 4304A,a general purpose unit,
with a frequency range of 25-1000MHz.It uses only one special element to
cover up to 500 watt, CW. The accuracy varies with frequency, but +-6 to
+-7% is typical. Photo
6 is a rare example of a Bird crossed needle meter, model 4342.The rear
of the unit has a line section that holds two elements simultaneously,
one in forward direction the other in reverse.
Where the two needles cross, the VSWR can be read. Models are also made for
measuring complex waveforms such as cellular digital transmissions,
and ones with built-in variable RF samplers to allow low level signals
to be measured with frequency counters, oscilloscopes, etc. Buying
second-hand: the pitfalls.
Like any moving coil metered instrument, they are susceptible to
physical shock. This usually manifests itself in a ‘balance’
problem. Hold the meter both vertical and horizontal. The needle should
stay at zero if all is well. If
it doesn’t, this will be an expensive repair, with replacement of the
entire meter assembly being the only option. The pivots and hairsprings
in the movement are prone to damage by sudden shock
With more sophisticated models, the question of calibration
becomes paramount, and unless you have access to accurate RF sources,
the cost involved in having a meter re-calibrated may make the purchase
price unrealistic. For calibration purposes, Bird manufacture RF
calorimeters with accuracies of +-1.25%.However, you are unlikely to see
one of these at a rally (and no, I don’t have one!). The elements are fairly
robust, having ptfe insulated backs and
gold-plated bodies. Too much RF can damage them, but the only way to
find out if it works is to try it in a known working meter. In
view of the cost of new Japanese/Chinese made wattmeter/vswr units and
dummy loads, second hand Bird equipment can be bought at reasonable
prices. Search the web for the company’s site, so you know what each
item can be expected to do. Finally,
as in all purchasing, caveat emptor
73
Steve M0OXR |








The 3B7C DXpedition to ST Brandon Island in the Indian Ocean
The expedition operated on the island for a large part of September 2007 and achieved over 135000 contacts on various amateur bands using voice, morse code and radio teletype modes of transmission. More information can be obtained from their website, (just type 3B7C into a search engine)

Don Field, G3XTT, a member of the expedition, came to our club on Thursday February 8th. to give a talk on last years very successful DXpedition to St. Brandon island in the Indian Ocean. Don is a an excellent and experienced speaker and the talk was very interesting and well presented. It was especially well received as we had already a screening of the official 3B7C DVD (courtesy of Ray, G4FON) in January, so Don's anecdotes and background really helped to give us a true feeing for what it was like to experience such an event first hand. Don also brought along QSL cards for some of the members who had managed to contact 3B7C. Don is pictured here (on the left), with our Secretary, Janet 2E0LLM, our President Barry G4AZN and our Chairman Ken M1SLH
Below are PIX of Richard Brett-Knowles G3AAT. He was kind enough to visit our Club on 13th March

He gave a most interesting talk on the early history of RADAR with the aid of
slides and old valved equipment also an AR88 Receiver powered by a rotary
converter. He was a most entertaining speaker and had some very interesting
stories about wartime exploits and how close we could have
been to defeat in our Island in the second world war.